Abstract

The power of the Tully-Fisher relation as a tool of observational cosmology has long been acknowledged. However, all attempts of unravelling the evolution of disc galaxies at high redshift have proven inconclusive. We demonstrate how rotation curves measured at the rest-wavelength of H_alpha can successfully shed some light unto the topic. Our sample of 21 galaxies at a mean redshift of z=0.9, the most distant sample so far, consists of mainly large isophotally selected late disc galaxies comparable to the Milky Way. These are amongst the largest in terms of disc scale lengths even compared to local galaxies. From this we conclude that the appearance of large disc galaxies must lie further back than ~8Gyr. We find that these galaxies have much higher surface brightnesses (1.44mag) than a local set of galaxies
with similar sizes. Their absolute magnitudes are only slightly brighter, though. Furthermore, combining the evolution in magnitude, size and surface brightness, we find that a scenario where galaxies grow inside-out is more consistent with the data than self-similar evolution. Moreover, the rotation velocities of the distant sample are systematically lower than the local sample, resulting in a lower average mass by a factor of ~2. The combination of those two effects results in an offset from the local Tully-Fisher relation of Delta_TF=-1.44mag towards brighter
magnitudes. Compared to similar data in the literature we find a consistent picture for the evolution of the Tully-Fisher relation with redshift:
Delta_TF=(0.19+-0.19)-(1.40+-0.32)z.
Total source numbers in the individual redshift bins are too small even taking all the available data together to meaningfully constrain the slope of the Tully-Fisher relation at high redshifts. The observed offset from the Tully-­Fisher relation is in good agreement with the
offset derived from numerical simulations by Steinmetz and Navarro (1999) at a redshift z~1.